Well a hokage on par with his student isn't good...that means he's gotten much weaker and/or orochimaru is crazily strong. I believe orochimaru to be one of the strongest characters in naruto and how sasuke "killed" him (temporarily) didn't make sense to me at all. But he didn't do much back then and obviously three years is enough to surpass the third if they were on par back then. And the first and second didn't have that much of an effect. Besides making the entire place a forest and making everything dark, the two really didn't do much, fighting wise...the third literally ran and caught them each with a kage bunshin for goodness sakes...
I agree with your point about obito though. It makes sense since he was kinda brainwashed by madara.
Wait, Obito and Madara did have a hand in it because of the Fox attack but didn't the Fox kill Minato?
Correct me if I'm wrong but, weren't we told that Karin was an Uzamaki a long time back? I mean maybe not literally related but you know seperated by time and clan mixups? That's why she has red hair and slightly different chakra ability.